Four healthy male subjects smoked two marijuana cigarettes or one marijuana cigarette and one placebo cigarette, or two placebo cigarettes on separate days in a random order crossover design. Each marijuana cigarette contained 2.8% delta-9-tetrahydrocannabinol (THC). Plasma hormones and THC were measured before and after each smoking session. Plasma LH was significantly depressed and cortisol was significantly elevated after smoking marijuana. Nonsignificant depressions of prolactin, FSH, testosterone and free testosterone and elevation of GH also occurred. Concurrent measures of subjective effects via subscales of the Addiction Research Center Inventory, Single Dose Questionnaire and a Visual Analog Scale were generally elevated. Significant impairment on a psychomotor performance task paralleled elevations in subjective effects, hormone effects and peak THC determinations. Although all the hormone effects were within normal basal ranges, interactions between these systems, and their effects on behaviour cannot be discounted.